Dynamic quality adjustment based on changing streaming constraints

ABSTRACT

A method and apparatus for dynamic quality adjustment of digital media based on changing streaming constraints is provided. A digital media server sends a digital media stream according to a set of streaming constraints to a requesting client. Audio and visual information may be sent to a requesting client together in a single stream, or separately in multiple streams. A client sends a request over a control network to the digital media server indicating information of a particular type is no longer desired. In response to receiving the signal, the video server ceases transmission of that particular type of information to the signaling client, thus relaxing streaming constraints. As a result of the techniques described herein, an improved quality digital presentation is available for the client and, consequently, when a viewer signals that a particular type of information is not desired, that particular type of information is not transmitted to the client, which thereby reduces the streaming constraints on a video streaming service, and improved quality digital media information may be sent to any client using the freed-up portion of the bandwidth previously allocated to the signaling client.

RELATED APPLICATION DATA

This application is a continuation-in-part application of copending U.S.application Ser. No. 09/128,224 filed on Aug. 3, 1998, which is acontinuation-in-part application of copending U.S. application Ser. No.08/859,860 filed on May 21, 1997, which is a continuation application ofU.S. application Ser. No. 08/502,480 filed on Jul. 14, 1995, now U.S.Pat. No. 5,659,539, all of which are incorporated herein by reference intheir entirety.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for processingaudio-visual information, and more specifically, to a method andapparatus for providing improved quality digital media in response torelaxed streaming constraints.

BACKGROUND OF THE INVENTION

In recent years, the media industry has expanded its horizons beyondtraditional analog technologies. Audio, photographs, and even featurefilms are now being recorded or converted into digital formats. Digitalmedia's increasing presence in today's society is not without warrant,as it provides numerous advantageous over analog film. As users of thepopular DVD format well know, digital media does not degrade fromrepeated use. Digital media can also either be delivered forpresentation all at once, as when leaded by a DVD player, or deliveredin a stream as needed by a digital media server.

As would be expected, the viewers of digital media desire at least thesame functionality from the providers of digital media as they now enjoywhile watching analog video tapes on video cassette recorders. Forexample, a viewer of a digital media presentation may wish to mute theaudio just as one might in using analog videotapes and videocassetterecorders. Currently, this is performed by adjusting the viewer's volumecontrols. However, as the server is unaware that audio information isnot desired by the viewer, the server still continues to transmit audioinformation to the viewer. In a distributed digital media environment,the resulting waste in available bandwidth on the digital media serveris considerable.

SUMMARY OF THE INVENTION

Techniques are provided for eliminating the waste in bandwidth on thedigital media server when a particular type of data is not desired to bereceived by a user. Extra value is provided to a viewer by utilizing thebandwidth previously allocated to the client to send improved qualityimages or additional information, such as closed-captioned information.According to one aspect of the present invention, a digital media streamis sent to a client according to a set of streaming constraints. In oneembodiment, the digital media stream contains both audio and visualinformation. According another embodiment, the digital media streamcontains only visual information and a separate audio stream is sent tothe client containing audio information. Next, a signal is receivedindicating a relaxation of streaming constraints corresponding to aparticular type of data in the digital media stream. In one embodiment,the signal indicates the client is not to receive audio information. Inanother embodiment, the signal indicates the client is not to receiveinformation of a particular type. In response to the signal, a set ofimproved quality media information is sent to the client.

According to one embodiment, a set of improved quality media informationmay be sent using the freed-up portion of the bandwidth previouslyallocated to the client. According to another embodiment, a set ofimproved quality media information may be sent to a first client usingthe freed-up portion of the bandwidth previously allocated to a secondclient. According to a further embodiment, the set of improved qualitymedia information includes closed-captioned information.

As a result of the techniques described herein, an improved qualitydigital media stream is available for presentation to a client and,consequently, when a viewer requests to discontinue an undesiredcomponent of a streaming video presentation, the undesired informationis not sent to the client, which thereby reduces the streamingconstraints on a video streaming service, and the improved quality mediainformation may be sent using the freed-up portion of the bandwidthpreviously allocated to the requesting client.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a block diagram of an audio-visual information delivery systemaccording an embodiment of the present invention;

FIG. 2 illustrates the various layers of a digital media file accordingto one embodiment of the present invention;

FIG. 3 illustrates the operation of a multiplexor according to anembodiment of the invention;

FIG. 4 is a flow chart illustrating the steps of dynamic qualityadjustment according to an embodiment of the invention; and

FIG. 5 illustrates the operation of a modified multiplexor according toan embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A method and apparatus for dynamic quality adjustment based on changingstreaming constraints is described. In the following description, forthe purposes of explanation, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one skilled in the art that the presentinvention may be practiced without these specific details. In otherinstances, well-known structures and devices are shown in block diagramform in order to avoid unnecessarily obscuring the present invention.

In the following description, the various features of the inventionshall be discussed under topic headings that appear in the followingorder:

I. System Overview

II. Digital Audio/Video File Structure

III. Multiplexor Operations

IV. Functional Operation

I. System Overview

FIG. 1 is a block diagram illustrating an audio-visual informationdelivery system 100 according to one embodiment of the presentinvention. Audio-visual information delivery system 100 contains aplurality of clients (1−n) 160, 170 and 180. The clients (1−n) 160, 170and 180 generally represent devices configured to decode audio-visualinformation contained in a stream of digital audio-visual data. Forexample, the clients (1−n) 160, 170 and 180 may be set top converterboxes coupled to an output display, such as a television.

As shown in FIG. 1, the audio-visual information delivery system 100also includes a stream server 110 coupled to a control network 120.Control network 120 may be any network that allows communication betweentwo or more devices. For example, control network 120 may be a highbandwidth network, an X.25 circuit or an electronic industry association(EIA) 232 (RS-232) serial line or an IP network.

The clients (1−n) 160, 170 and 180, also coupled to the control network120, communicate with the stream server 110 via the control network 120.For example, clients 160, 170 and 180 may transmit requests to initiatethe transmission of audio-visual data streams, transmit controlinformation to affect the playback of ongoing digital audio-visualtransmissions, or transmit queries for information. Such queries mayinclude, for example, requests for information about which audio-visualdata streams are currently available for service.

The audio-visual information delivery system 100 further includes avideo pump 130, a mass storage device 140, and a high bandwidth network150. The video pump 130 is coupled to the stream server 110 and receivescommands from the stream server 110. The video pump 130 is coupled tothe mass storage device 140 such that the video pump 130 retrieves datafrom the mass storage device 140. The mass storage device 140 may be anytype of device or devices used to store large amounts of data. Forexample, the mass storage device 140 may be a magnetic storage device,an optical storage device, or a combination of such devices. The massstorage device 140 is intended to represent a broad category ofnon-volatile storage devices used to store digital data, which are wellknown in the art and will not be described further. While networks 120and 150 are illustrated as different networks for the purpose ofexplanation, networks 120 and 150 may be implemented on a singlenetwork.

The tasks performed during the real-time transmission of digital mediadata streams are distributed between the stream server 110 and the videopump 130. Consequently, stream server 110 and video pump 130 may operatein different parts of the network without adversely affecting theefficiency of the system 100.

In addition to communicating with the stream server 110, the clients(1−n) 160, 170 and 180 receive information from the video pump 130through the high bandwidth network 150. The high bandwidth network 150may be any type of circuit-style network link capable of transferringlarge amounts of data, such as an IP network.

The audio-visual information delivery system 100 of the presentinvention permits a server, such as the video pump 130, to transferlarge amounts of data from the mass storage device 140 over the highbandwidth network 150 to the clients (1−n) 160, 170 and 180 with minimaloverhead. In addition, the audio-visual information delivery system 100permits the clients (1−n) 160, 170 and 180 to transmit requests to thestream server 110 using a standard network protocol via the controlnetwork 120. In one embodiment, the underlying protocol for the highbandwidth network 150 and the control network 120 is the same. Thestream server 110 may consist of a single computer system, or mayconsist of a plurality of computing devices configured as servers.Similarly, the video pump 130 may consist of a single server device, ormay include a plurality of such servers.

To receive a digital audio-visual data stream from a particular digitalaudio-visual file, a client (1−n) 160, 170 or 180 transmits a request tothe stream server 110. In response to the request, the stream server 110transmits commands to the video pump 130 to cause video pump 130 totransmit the requested digital audio-visual data stream to the clientthat requested the digital audio-visual data stream.

The commands sent to the video pump 130 from the stream server 110include control information specific to the client request. For example,the control information identifies the desired digital audio-visualfile, the beginning offset of the desired data within the digitalaudio-visual file, and the address of the client. In order to create avalid digital audio-visual stream at the specified offset, the streamserver 110 may also send “prefix data” to the video pump 130 and mayrequest the video pump 130 to send the prefix data to the client. Prefixdata is data that prepares the client to receive digital audio-visualdata from the specified location in the digital audio-visual file.

The video pump 130, after receiving the commands and control informationfrom the stream server 110, begins to retrieve digital audio-visual datafrom the specified location in the specified digital audio-visual fileon the mass storage device 140.

The video pump 130 transmits any prefix data to the client, and thenseamlessly transmits digital audio-visual data retrieved from the massstorage device 140 beginning at the specified location to the client viathe high bandwidth network 150.

The requesting client receives the digital audio-visual data stream,beginning with any prefix data. The client decodes the digitalaudio-visual data stream to reproduce the encoded audio-visual sequence.

II. Digital Audio/Video File Structure

Having described the system overview of the audio-visual informationdelivery system 100, the format of the digital media, or audio-visual,file structure will now be described. Digital audio-visual storageformats, whether compressed or not, use state machines and packets ofvarious structures. The techniques described herein apply to all suchstorage formats. While the present invention is not limited to anyparticular digital audio-visual format, the MPEG-2 transport filestructure shall be described for the purposes of illustration.

Referring to FIG. 2, it illustrates the structure of an MPEG-2 transportfile 104 in greater detail. The data within MPEG file 104 is packagedinto three layers: a program elementary stream (“PES”) layer, atransport layer, and a video layer. These layers are described in detailin the MPEG-2 specifications. At the PES layer, MPEG file 104 consistsof a sequence of PES packets. At the transport layer, the MPEG file 104consists of a sequence of transport packets. At the video layer, MPEGfile 104 consists of a sequence of picture packets. Each picture packetcontains the data for one frame of video.

Each PES packet has a header that identifies the length and contents ofthe PES packet. In the illustrated example, a PES packet 250 contains aheader 248 followed by a sequence of transport packets 251-262. PESpacket boundaries coincide with valid transport packet boundaries. Eachtransport packet contains exclusively one type of data. In theillustrated example, transport packets 251, 256, 258, 259, 260 and 262contain video data. Transport packets 252, 257 and 261 contain audiodata. Transport packet 253 contains control data. Transport packet 254contains timing data. Transport packet 255 is a padding packet.

Each transport packet has a header. The header includes a program ID(“PID”) for the packet. Packets assigned PID 0 are control packets. Forexample, packet 253 may be assigned PID 0. Control packets containinformation indicative of what programs are present in the digitalaudio-visual data stream. Control packets associate each program withthe PID numbers of one or more PMT packets, which contain Program MapTables. Program Map Tables indicate what data types are present in aprogram, and the PID numbers of the packets that carry each data type.Illustrative examples of what data types may be identified in PMTpackets include, but are not limited to, MPEG2 video, MPEG2 audio inEnglish, and MPEG2 audio in French.

In the video layer, the MPEG file 104 is divided according to theboundaries of frame data. As mentioned above, there is no correlationbetween the boundaries of the data that represent video frames and thetransport packet boundaries. In the illustrated example, the frame datafor one video frame “F” is located as indicated by brackets 270.Specifically, the frame data for frame “F” is located from a point 280within video packet 251 to the end of video packet 251, in video packet256, and from the beginning of video packet 258 to a point 282 withinvideo packet 258. Therefore, points 280 and 282 represent the boundariesfor the picture packet for frame “F”. The frame data for a second videoframe “G” is located as indicated by brackets 272. The boundaries forthe picture packet for frame “G” are indicated by bracket 276.

Many structures analogous to those described above for MPEG-2 transportstreams also exist in other digital audio-visual storage formats, suchas MPEG-1, Quicktime, and AVI. In one embodiment, indicators of videoaccess points, time stamps, file locations, etc. are stored such thatmultiple digital audio-visual storage formats can be accessed by thesame server to simultaneously serve different clients from a widevariety of storage formats. Preferably, all of the format specificinformation and techniques are incorporated in the stream server. All ofthe other elements of the server are format independent.

III. Multiplexor Operations

It is often desirable to merge several digital media presentations, eachpresentation in a separate digital media stream, into one streamcontaining the combined digital media presentations. This merger allowsa user to select different digital media presentations to watch from asingle digital media stream. FIG. 3 illustrates a multiplexor 310, whichis a digital media component that performs the operation of mergingmultiple digital media streams into a single digital media stream. Asmultiplexors are well understood to those in the art, description inthis section will be limited to the extent that it facilitatesunderstanding of their use in optimizing mute operations in amultiplexed stream environment, which will be described in detail below.

As FIG. 3 shows, a multiplexor 310 has multiple inputs and a singleoutput. The inputs to the multiplexor are called Single ProgramTransport Streams (“SPTS”), labeled as 320, 322, and 324, and the outputis called a Multiple Program Transport Stream (“MPTS”), which is labeledas 330. A Single Program Transport Stream 320, 322, and 324 is a digitalmedia stream that is encoded with audio and video data for one videopresentation. Alternately, a Multiple Program Transport Stream 330 is adigital media stream that is encoded with audio and video data formultiple video presentations. Thus, a Single Program Transport Stream320, 322, and 324 is analogous to a single channel on TV, whereas aMultiple Program Transport Stream 330 is analogous to a cable network.

When the individual SPTSs 320, 322, and 324 are combined, themultiplexor 310 examines the PID in each transport packet to ensure thateach PID referenced in the control packets is unique. In the case whenpackets from different SPTSs 320, 322, and 324 use the same PID, themultiplexor 310 remaps the PIDs to unique numbers to ensure that eachpacket can easily be identified as belonging to a particular SingleProgram Transport Stream 320, 322, and 324. As each audio and videopacket is guaranteed to have a unique PID, the video presentation towhich the packet corresponds may be easily identified by examining thePID 0 control packets in the MPTS 330. Thus, as the multiplexor 310 mustexamine each table in the PID 0 control packets and all tables ofpackets references in the PID 0 control packets to ensure all referencedpackets have a unique PID number, it also can easily identify all audiopackets corresponding to a particular SPTS 320, 322, and 324.

IV. Functional Operation

A client may reduce the amount of a particular type of informationcontained in the digital media presentation that is received. In oneembodiment, the amount of a particular type of information required bythe client is reduced as the result of altering the presentationcharacteristics to a state requiring less of the particular type ofinformation, such as when reducing the video resolution, or switchingthe sound output from stereo to mono. In another embodiment, theparticular type of information is not required at all, such as when aclient mutes the audio portion of a presentation. It is beneficial forthe stream server 110 to reclaim the bandwidth previously allocated todelivering that particular type of information to the client. This extrabandwidth can be used to improve the quality of the digital mediapresentation, or to send additional information, such asclosed-captioned information.

An exemplary description will now be provided with reference to FIG. 4to illustrate the process of reclaiming unused bandwidth wherein theclient mutes the audio in a digital media presentation. The client 160sends a signal through the control network 120 to the stream server 110to indicate that audio data is not to be sent to the client. The signalis sent using existing communication protocols, such as Real TimeStreaming Protocol (“RTSP”).

In one embodiment, the stream server 110 operates in a multiplexedenvironment, or an environment in which audio and visual data is sent tothe client in a single stream, such as in MPEG. In response to receivingthe signal, a multiplexor is used to examine and identify the packetsfor the particular SPTS being muted. The multiplexor then discards theidentified audio packets for the muted SPTS and does not combine them inthe output stream.

In another embodiment, the stream server 110 still operates in amultiplexed environment, but in response to receiving the signal, amodified multiplexor 510 is used to examine and identify the packets forthe particular SPTS being muted, as shown in FIG. 5. The modifiedmultiplexor 510 operates in substantially the same way as described inthe prior section, except that it operates with only one input SPTS 520.The modified multiplexor 510 then filters and discards the identifiedaudio packets for the input SPTS 520. The resulting output stream 530from the modified multiplexor 510 contains the original mediapresentation, but not any audio packets, from the input SPTS 520.

In still another embodiment, the stream server 110 operates in asplit-stream environment, or an environment in which audio and visualdata are sent to the client in separate streams. In response toreceiving the signal, the stream server 110 continues sending the videostream, but pauses or stops sending the audio stream to the signalingclient. As the video is sent in a different stream to the signalingclient than the audio, stopping the audio stream will not interrupt thevideo presentation to the signaling client.

As audio packets for the muted digital video stream are no longer sentto the client, the bandwidth previously allocated to the signalingclient can be reclaimed. Accordingly, streaming constraints on thestream server 110 are reduced.

As mentioned previously, reclaiming bandwidth as a result of a clientsignaling to discontinue transmission of a particular type ofinformation is not limited to audio information. A client may signal toindicate any particular type of information contained within the digitalmedia stream is no longer to be sent to that client. For example, theclient signals to indicate that visual information in no longer to besent. Accordingly, the reclaimed bandwidth on the stream server 110 maybe used to send improved quality information of the remaining types ofinformation contained in the digital media stream, or send additionalinformation. For example, if a client signals to indicate visualinformation is not to be sent, improved quality audio information may besent. Examples of improved quality audio information include, but arenot limited to, sending audio information in a format such as THX orDolby, sending additional sound tracks, or sending information insurround sound.

In one embodiment, bandwidth reclaimed on the stream server 110 from oneclient may be utilized by any client of the stream server 110. Inanother embodiment, bandwidth reclaimed on the stream server 110 fromone client may only be used by that client.

As mentioned above, one use of the reclaimed bandwidth is to provideimproved quality. The quality of the video may be improved by modifyingone or more of a video's characteristics. Examples of improving thequality of a video include, but are not limited to, increasing the rateof frame transmission, increasing color depth, and increasing the pixeldensity. In addition to, or instead of, increasing the quality of thevideo, the reclaimed bandwidth may be used to send or improve other dataassociated with the video. For example, the reclaimed bandwidth may beused to send closed-captioned information, additional information, orotherwise alter the appearance of the video in some form.

In other embodiments, the quality of the video may be improved throughimproved quantization. Improved quantization is achieved by collapsingsimilar states into a single state, thereby allowing more unique statesto be identified. For example, assume each color used in a digital videopresentation is assigned a 24 bit number. By grouping similar colorstogether and assigning them the same 24 bit number, more unique colorsmay be identified for use in the digital video with 24 bits.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of the invention. Thespecification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense.

1. A method of operating a stream server, the stream server causing datastreams to be provided from one or more stored audio/visual files, themethod comprising: receiving a signal from a client device, said signalincluding an indication of a client requested presentation action that,when put into effect by the stream server, involves reducing a data rateof audio data of a first audio/visual stream being sent from the streamserver to the client device or eliminating the transmission of the audiodata of the first audio/visual stream to the client device; implementingthe client requested presentation action, said act of implementing theclient requested presentation action including reducing the data rate ofthe audio data of the first audio/visual stream or eliminating thetransmission of the audio data of the first audio/visual stream to theclient device; and determining an amount that a data rate of a secondaudio/visual data stream may be increased as a result of an effect ontransmission bandwidth corresponding to the reduction in the data rateof the audio data of the first audio/visual stream or the elimination ofthe audio data of the first audio/visual stream.
 2. The method of claim1, wherein said indication comprises: an indication that audio be muted.3. A method of operating a stream server, the stream server causing datastreams to be provided from one or more stored audio/visual files, themethod comprising: the stream server providing to one or more clientdevices a first audio/visual stream and a second audio/visual stream;receiving a signal from one of the client devices, said signal includingan indication of a client requested presentation action that, when putinto effect by the stream server, involves reducing a data rate of audioor video data of the first audio/visual stream or eliminating thetransmission of the audio or video data of the first audio/visualstream; implementing the client requested presentation action, said actof implementing the client requested presentation action includingreducing a data rate of audio or video data of the first audio/visualstream or eliminating the transmission of the audio or video data of thefirst audio/visual stream; and determining whether a third audio/visualstream may be streamed as a result of an effect on transmissionbandwidth corresponding to a reduction in the data rate of audio orvideo data of the first audio/visual stream or eliminating thetransmission of the audio or video data of the first audio/visualstream.
 4. The method of claim 3, wherein said indication comprises: anindication that audio be muted.
 5. The method of claim 3, furthercomprising: including both said first and second audio/visual streams indifferent Single Program Transport Streams, each of said differentSingle Program Streams being part of a Multiple Program Transport Streamwhich includes both of said different Single Program Transport Streams.6. A computer program product, comprising instructions that, when putinto effect, enable a stream server device that causes data streams tobe provided from one or more stored audio/visual files: to interpret anindication of a client requested presentation action that will affectthe bandwidth requirements of audio data of a first audio/visual streamthat the stream server is streaming to the client device; to identifythe action from the indication and put the action into effect, with theresult that the rate of the audio data of the first audio/visual streamto the client is changed; and to determine an amount that a videostreaming rate of a second audio/visual data stream should be changed asa result of bandwidth effects of the changed rate for the audio data ofthe first audio/visual stream, and to change video streaming rate of thesecond audio/visual data stream according to the amount.
 7. The computerprogram product of claim 6, wherein the instructions to enable thestream server to interpret the indication as an action that involveschanging the quality of, or eliminates, the audio stream being streamedto the client comprise: instructions to enable the stream server tointerpret the indication to mean that the audio stream should be changedfrom mono to stereo, or vice versa, or that the audio stream should bemuted or unmuted.
 8. The computer program product of claim 6, whereinthe instructions to enable the stream server to determine an amount thata video streaming rate of a second audio/visual stream should be changedas a result of bandwidth effects further comprise: instructions toenable the stream server to determine how much bandwidth is freed up orconsumed by putting the action into effect.
 9. A stream server systemfor providing data streams from one or more stored audio/visual files,comprising: means for receiving a signal from a client device, saidsignal including an indication of a client requested presentation actionthat, when put into effect, reduces or eliminates the rate at which theclient receives audio data of a first audio/visual stream; means foridentifying the action from the indication and putting the action intoeffect, with the result that the client device receives the audio dataof the first audio/visual stream at a reduced or eliminated rate; andmeans for making a determination of an amount that a rate of a secondaudio/visual data stream may be increased as a result of bandwidtheffects of the reduced or eliminated rate for the audio data of thefirst audio/visual stream.
 10. A stream server system for providing datastreams from one or more stored audio/visual files, comprising: meansfor streaming first and second audio/visual streams; means for receivinga signal from a client device, said signal including an indication of aclient requested presentation action that, when put into effect, reducesor eliminates the rate at which the client receives audio data of afirst audio/visual stream; means for identifying the action from theindication and putting the action into effect, with the result that theclient device receives the audio data of the first audio/visual streamat a reduced or eliminated rate; and means for making a determination ofwhether a third audio/visual stream may be streamed as a result ofbandwidth effects of the reduced or eliminated rate for the audio dataof the first audio/visual stream.
 11. A stream server system forproviding data streams from one or more stored audio/visual files,comprising: means for receiving a signal from a client device, saidsignal including an indication of a client requested presentation actionthat, when put into effect, increases a rate at which the clientreceives audio data of a first audio/visual stream; means foridentifying, the action from the indication and putting the action intoeffect, with the result that the client device receives the audio dataof the first audio/visual stream at an increased rate; and means formaking a determination of an amount that a rate of a second audio/visualdata stream should be reduced as a result of bandwidth effects of theincreased rate for the audio data of the first audio/visual stream. 12.A method comprising: receiving a signal from a client device, saidsignal including an indication of a client requested presentation actionthat, when put into effect, involves reducing a data rate of audio dataof a first audio/visual stream being sent to the client device oreliminating the transmission of the audio data of the first audio/visualstream to the client device; the act of reducing the data rate of theaudio data of the first audio/visual stream or eliminating thetransmission of the audio data of the first audio/visual stream to theclient device including providing a stream of packets as part of apacket flow to a multiplexing device, said stream of packets includingdata packets which can be sent to the client device in said audio dataof the first audio/visual stream; and operating the multiplexer toperform a filtering operation on said stream of packets to reduce oreliminate the data rate of the audio data of the first audio/visualstream.